1. Field of the Invention
The present invention relates to an optical element that creates a minute optical spot using a minute structure and an optical spot position adjusting method. Specifically, the invention relates to the optical element that is used for recording and/or reproducing information using near-field light, and the optical spot position adjusting method in the optical element.
2. Description of the Related Art
In recent years, in optical recording and reproducing techniques, the use of a near-field light generating structure is variously proposed in order to obtain a minute optical spot. In order to realize the recording/reproduction using near-field light, a solid immersion lens or a solid immersion mirror is used as a condensing element, and a minute spot is made to be close to a recording medium so that an evanescent wave and the recording medium interact with each other. As a result, recording or reproducing density of information is heightened.
Since near-field light is generated on a condensing surface of the optical element such as the solid immersion lens or the solid immersion mirror, a minute structure whose size is not more than 1 μm is formed, and thus a condensing spot of a light beam should be accurately matched with the minute structure.
For this reason, Japanese Patent Application Laid-Open No. 2000-293877 discloses that a plurality of photodiodes are formed around a minute structure provided to a condensing surface of an optical element, and a light beam is emitted to the optical element so that an emitted position of the light beam is adjusted based on a detected result by means of the photodiodes. Further, Japanese Patent Application Laid-Open No. 2002-236087 discloses that a minute structure is formed on a metallic thin film provided to a condensing surface of an optical element, a light beam is emitted to the optical element so that its reflected light is detected, and intensity of the reflected light is adjusted so as to be minimum.
In recent years, an optical element, where a plurality of minute structures are formed on a metallic thin film provided to a condensing surface and an optical spot is matched with any one of the minute structures in order to facilitate position adjustment of the optical spot, is proposed.
In the adjusting method disclosed in Japanese Patent Application Laid-Open No. 2000-293877, a plurality of photodiodes are formed around the minute structure, but since the minute structures have size of not more than 1 μm and the gap therebetween is not more than 2 μm, there is a problem that no a space where the photodiodes are formed around the minute structures.
Further, in the adjusting method disclosed in Japanese Patent Application Laid-Open No. 2002-236087, when a plurality of minute structures are formed on the metallic thin film which is formed uniformly, the intensity of the reflected light is hardly different between the thin film portion and the minute structures, and thus there is a problem that the positions of the minute structures cannot be actually detected.